Drying roll



R. R, LAING DRYING ROLL .March 21; 1939.

Filed July 1, 1937 INVENTOR. 4 RICHARD l2. Lfl/NG.

WITNESSES:

ATTORNEY.

Patented Mar. 21, 1939 I name non. Richard R. Laing, Fairiieid, Conm, assignor to Aluminum Company of America,

Pittsburgh,

Pa., a corporation of Pennsylvania Application July 1', 1931, Serial No. 151,441

. 'i This invention relates to'the manufacture of cellulose material, and more particularly to a method of drying cellulose materialand to drying machinery used in its manufacture. 5 In the course of the manufacture of sheets or films of non-fibrous cellulose material, such as that sold under the name Cellophane, it is customary to subject the sheets to a drying and stretching operation. This is ordinarily done by passing them over a succession of heated rolls having a somewhat tacky surface or a surface to which the sheets will adhere. The rolls are in the form of metal cylinders mounted to rotate about their longitudinal axes, and may be heated 15 by any of a number of methods, although the method generally used is to run hot water through them.

Prior to my invention, iron and steel drying 'rolls having a coating of varnish have been used for this purpose. However, such rolls have presen'ted several difiiculties. The coating of varnish wears away in use and must be renewed comparatively frequently. Also, the adhesiveness of the varnish coating varies with the temperature of 25 the roll; the colder the roll is, the less adhesive I is its surface, so' that it is difficult to'obtain uniform results. Furthermore, the individual rolls do not heat uniformly throughout, the result' being that the drying effect of any one roll on the cellulose material may vary, depending on what portion of the roll comes in contact with the material and on the temperature of that portion.

,It has been proposedto make the rolls of aluminum because ,this metal conducts heat more ever, such rolls have not been entirely satisfactory, chiefly because. of the fact that in the aluminum and raise burrs on the roll surfaces. These burrs mar the cellulose sheets which subsequently pass over them. Another difficulty encountered with aluminum rolls is that their externalsurface is corroded by the treating solutions present on the cellulose material, and their internal surface may be corroded by the water which heats-the rolls, if this method of heating is used.

It is an object of my invention to provide an aluminum drying roll for use in the drying of cellulose films or sheets, the roll having an external surface which is of atype which will not be susceptible to burring by knife edges when cellureadily anduniformly than iron or steel. Howtangled among the rolls and must be cut away with sharp knives which frequently score the lose material must be cut away from the roll.

Another object of the invention is to provide an aluminum drying roll having a hard, adherent, abrasion-resistant coating consisting substantially of aluminum oxide. A further object of my 5 invention is to provide-a method of drying cellulose material in which'the said material passes over a heated aluminum cylinder having a hard, adherent, abrasion-resistant coating consisting substantially of aluminum oxide. Other objects of the invention will be apparent from the following speciflcation and claims, and from the accompanying drawing.

I have discovered that aluminum or aluminum base alloy drying rolls'which are provided with a coating of the type generally referred to in the art as an oxide coating", have properties which make them highly suitable for use in the manufacture of cellulose films or sheets. The term "oxide coating 'is used herein to designate an artificially produced coating consisting substantially of aluminum oxide on aluminum or aluminum base alloys, which coating is formed by a chemical or electrochemical treatment, and. is of substanial thickness, as distinguished from the 5 thin film of' aluminum oxide which is naturally formed on aluminum surfaces by contact with the air. Such oxide coatings may be produced on aluminum surfaces by a number of well known methods, such as by immersing the article to be coated for a short time in a hot solution of an alkali carbonate containing a small amount of an inhibitor, such as a chromate, or by making the article the anode in an electrolytic cell in which the electrolyte consists of an acid solution, such as sulfuric acid, chromic acid, oxalic acid, or mixtures of these acids.

The characteristics of the coating vary somewhat with the methods used to produce them, particularly as to hardness. For my purposes, I 40 prefer to use the methods which produce the harder, more adherent types of coating, and have found especially suitable the method in which the aluminum article to be coated is made the anode in an electrolyte containing about 5 to 35 per cent 5 of sulfuric acid. However, other methods can also be used satisfactorily, and it is to be understood that I do not intend my invention to be limited to an oxide coating produced by any particular method.

,Oxide coatings of the character produced by such methods are ordinarily hard. adherent, abrasion-resistant, and somewhat absorptive or adsorptive. Drying rolls equipped-with such coatings have a surface to which sheets of cellulose 55 material will adhere slightly during their passage over the rolls without the necessity of using varnish or similar substances on the roll surfaces. The properties of the coating may be modified to some extent, if desired, by treatment in hot water for a short time to render the coating less pervious and absorptive or adsorptive. The water should preferably be at boiling temperature, although satisfactory results can be obtained in water at temperatures as low as 80 C. The time of treatment in hot water may also vary in duration. Periods of from 5 to 30 minutes may be satisfactory, depending'upon the initial characteristics of the coating and on the extent to which it is desired to alter those characteristics.

It may be desirable that-the frictional resistance of some of the drying rolls vary from that of other rolls in the same drying machinery. This result can be accomplished readily in accordance with my invention by controlling such variable factors as the type of treatment used to produce the oxide coating and the duration of the treatment in boiling water, if such treatment is used.

Generally, rolls which have been subjected to a boiling water treatment offer less frictional resistance to the cellulose material than oxide coated rolls which have not been'so treated. The

ing their passage over the rolls.

The invention will. be found described with reference to the accompanying drawing, in which a drying roll prepared in accordance with my invention is illustrated, part of the rollbeing cut" away to show the coating.

In the drawing, the'dryingroll is shown as com prising a hollow aluminum cylinder 1 having on its external surface a coating 2 consisting sub away tangled cellulose material from :the'in a- 'chinery, will not burr or develop rough-edges;

stantially of aluminum mride. 'It will'be appreci-- ated that the thickness of the; coating is exaggerated'for the purposes of illustration. In 2.0- tual practice, a coating of from .0005 to .001 of an inch in thickness is ordinarily suillcient. However, any desired thickness of coatingcan' be used. Although, in the drawing, the oxide coating is shown only on the external surface of -the, cylinder, it will be appreciated that other portions of the roll,.such as the interior, may alsobe coated to advantage. y

it may be scored by the sharp'knives used to out They offer proper frictional resistance to-the'jcel-' lulose material passing over them,'insuring eflicie'nt'drying and stretching of the material, and the material may be readily stripped from tion of heat is obtained throughout.

As a specific example of my invention, an aluminum base alloy drying roll cylinder was provided with an oxide coating by making it the anode in an electrolytic cell in which a 15 per cent solution of sulfuric acid constituted the electrolyte. A current having a density of 1-5 amperes' per square foot of cylinder surface to be coated was applied for minutes, with'the electrolyte maintained at a temperature of 70 C. The cylinder was then removed from the electrolyte, rinsed with water, and dried.

In another example of the invention, an aluminum base alloy drying roll cylinder was provided with an oxide coating, as described in the previous paragraph, and was then immersed in boiling water for 5 minutes, after which it was removed from the water and dried.

As used hereinabove and in the appended claims, the term aluminum includes aluminum and aluminum base alloys.

I claim:

1. A drying roll for drying non-fibrous cellulose material, said roll comprising an aluminum v has been immersed in water ata temperatureof to centigrade for at least 5 minutes.

3. In, the p'roductionof nonfibrous cellulose sheet, the step comprising passing such cellulose sheet over aheated aluminum-surface, said surface having a hard-adherent, abrasion-resistant mcoatingconsisting substantially of aluminum oxide.

4.1 In the production of'non-fibrous cellulose sheet, the step comprising drying such cellulose sheetby passing it over a heated aluminum surface, said surface'havinga hard, adherent, abra sion-resistantcoating consisting" substantially of aluminum oxide.

5. In the production of vnon-fibrous'c'ellulosic same j over a heated" anodized aluminum surface.

' r 6'. In the roductionof non-'iibrou's' ellulo Drying rolls embodying my'invention -.have a' 0 s10 hard, abrasion-resistant coatingwhich, thougnf m s over a {heated anodized aluminum surface.-

pelliclesathe step which'kcomprises'drying said,

anodized surface.

pellicles, thej-step which comprises passing the' 

